More from WebMD

Oct. 26, 2011 -- Just ask anyone who has ever tried to shed extra pounds: Losing weight can be hard, but it's keeping this extra weight off that is often most daunting.

Now new research in the New England Journal of Medicine sheds some light on why, and the answer is not lack of willpower. It seems that our hormones -- at least those involved in appetite regulation -- may be setting us up to fail.

In a new study, 50 overweight or obese people went on a low-calorie diet for 10 weeks. Researchers measured levels of several key hormones involved in appetite control before they started the diet, after they completed the diet, and then again 62 weeks later.

They found that changes in the hormonal mix tip the scale toward hunger and weight regain. Up to a year after weight loss, there are increases in the "hunger hormone" ghrelin and reductions in other hormones such as leptin that could promote weight gain.

Hormones and Eating

Gherlin is the "go" hormone that tells us to eat. Leptin is the hormone that tells us to stop eating. More ghrelin and less leptin set the stage for weight regain. Reductions in other hormones such as peptide YY and cholecystokinin also help favor weight regain after weight loss.

From an evolutionary standpoint, these changes are supposed to prevent starvation when food is hard to come by. But "in an environment in which [high-calorie] food is abundant and physical activity is largely unnecessary, the high rate of relapse after weight loss is not surprising," the researchers state.

"The findings explain why most people find it difficult to maintain weight loss long term," study researcher Joseph Proietto, MBBS, PhD, tells WebMD in an email. Proietto is a professor of medicine at University of Melbourne, Australia. "It may also explain why public health measures adopted so far have generally failed to reduce obesity prevalence."

Does this mean weight regain is inevitable? No, Proietto says, "but published evidence shows that most people have regained lost weight by five years."

Several medications are being studied that may help combat some of these hormonal changes. "Until we have appetite suppressants that are safe to use long term, studies show that the following behaviors are associated with better weight loss maintenance: weigh yourself regularly; eat breakfast; exercise at least one hour per day; and eat a low-fat diet," Proietto says.

Second Opinion

"This is a really important study," says Scott Kahan, MD, an obesity expert at Johns Hopkins University in Baltimore. "It is clear from this study and many others that weight regain is not a problem of willpower."

"Things change hormonally, metabolically, and otherwise after you gain weight so even if you take it off, things don't go always go back to baseline," he says.

These findings further stress the importance of trying to prevent weight gain and obesity in the first place.

"It is not enough to throw a lot of resources at treating obesity, we need to focus on prevention," he says.

Louis Aronne, MD, founder and director of the Comprehensive Weight Control Program at New York-Presbyterian Hospital/Weill Cornell Medical Center, agrees.

"[Weight regain] is not your fault," he says. "Achieving weight loss and maintaining that loss is really complex and we need new approaches to treatment including medications."